These days, a touch panel is in widespread use for electronic devices such as a mobile phone, car navigation equipment, a personal computer, and a terminal of a bank etc. The touch panel allows a user to enter a touched position (contact position) by touching the touched position with a fingertip, a pen tip, or the like while visually recognizing an image displayed on a display screen constituted by a liquid crystal display panel etc. Recently, various types of touch panel have been proposed based on a detection principle for detecting a touched position. Among these touch panels, an electrostatic capacitive touch panel is suitably used because it has a simple mechanism, can be manufactured at low cost, and is relatively easily increased in size. Attention has been paid to, particularly, a technique of an in-cell electrostatic capacitive touch panel realized by combining a touch panel with a liquid crystal display device. This is because the in-cell electrostatic capacitive touch panel remarkably contributes to reduction in manufacturing cost and reduction in thickness.
FIG. 14 is an explanatory view schematically explaining an electrostatic capacitive touch panel. (a) of FIG. 14 illustrates a state where the electrostatic capacitive touch panel is combined with a liquid crystal display device so that the electrostatic capacitive touch panel is present above the liquid crystal display device. (b) of FIG. 14 schematically illustrates a configuration of electrodes of the electrostatic capacitive touch panel. (c) of FIG. 14 illustrates an operational principle of the electrostatic capacitive touch panel.
As illustrated in (a) of FIG. 14, a touch panel 100 is provided via a slight space 194 above a display device such as a liquid crystal display device 191, and a surface of the touch panel 100 is covered with a cover glass 193. When a specific position on the cover glass 193 is touched with a fingertip 194, the touched position is detected.
(b) of FIG. 14 illustrates a configuration example of electrodes of the touch panel 100. In (b) of FIG. 14, 110(1), 110(2), . . . , and 110(n) represent respective driving electrodes. Each of the driving electrodes is constituted by a plurality of rhombic electrodes connected in an X-axis direction (in a traverse direction of FIG. 14). The driving electrodes 110(1), 110(2), . . . , and 110(n) are electrically insulated from one another. The reference numeral “110” in (b) of FIG. 14 represents a group of all of the plurality of driving electrodes 110(1) through 110(n). The all of the plurality of driving electrodes 110(1) through 110(n) are described as a driving electrode group 110. Further, “n” of the driving electrode 110(n) is determined in accordance with a size of the touch panel. The driving electrode 110(n) generally means that a plurality of driving electrodes are present.
Similarly, in (b) of FIG. 14, 120(1), 120(2), . . . , and 120(m) represent respective sensing electrodes. Each of the sensing electrodes is constituted by a plurality of rhombic electrodes connected in a Y-axis direction (in a longitudinal direction of FIG. 14). The driving electrodes 120(1), 120(2), . . . , and 120(m) are electrically insulated from one another. The reference numeral “120” in (b) of FIG. 14 represents a group of all of the plurality of sensing electrodes 120(1) through 120(m). The all of the plurality of sensing electrodes 120(1) through 120(m) are described as a sensing electrode group 120. Further, “m” of the sensing electrode 120(m) is determined in accordance with the size of the touch panel. The sensing electrode 120(m) generally means that a plurality of sensing electrodes are present.
(c) of FIG. 14 illustrates a cross-sectional view taken along A-A′ line of (b) of FIG. 14, and schematically illustrates a case where the touch panel 100 is “not touched” with a fingertip etc. (a left part of (c) of FIG. 14) and a case where the touch panel 100 is “touched” with a fingertip etc. (a right part of (c) of FIG. 14). In (c) of FIG. 14, arrow lines schematically represent lines of electric force between the driving electrode 110 (1) to which a driving voltage is being applied and the sensing electrodes 120(1) and 120(2). As is clear from (c) of FIG. 14, when the touch panel is touched with a fingertip etc., some of the lines of electric force are grounded via the fingertip. This reduces capacitance between the driving electrode and the sensing electrodes. Such change in the capacitance is detected, so that a position touched by the fingertip etc. is detected.
Patent Literature 1 discloses a driving circuit of an electrostatic capacitive touch panel typified by the electrostatic capacitive touch panel illustrated in FIG. 14. FIG. 15 is an explanatory view explaining the driving circuit disclosed in Patent Literature 1. (a) of FIG. 15 is a diagram illustrating a configuration of the driving circuit. (b) of FIG. 15 is a timing chart explaining an operation of the driving circuit. (c) of FIG. 15 is a table explaining (i) steps shown in the timing chart and (ii) an operational state of the driving circuit. Note that, for convenience of explanation, (b) of FIG. 15 is partially modified from the drawing of Patent Literature 1 (specifically, steps 1 through 7 are added to the drawing of Patent Literature 1). Note also that (c) of FIG. 15 is a newly-added explanatory drawing which is not disclosed in Patent Literature 1.
In (a) of FIG. 15, the reference numeral “100” represents a driving electrode. The driving electrode 100 is connected to a voltage supply source 101. In (a) of FIG. 15, the reference numeral “104” represents a sensing electrode. The sensing electrode 104 is connected via a capacitor 105 to the driving electrode 100. The sensing electrode 104 is connected to a sampling switch 401, a storage capacitor 402, a reset switch 404, and an output amplifier 403. The sampling switch 401 and the reset switch 404 are controlled by a control circuit 108.
When the reset switch 404 is tuned off while the voltage supply source 101 is applying a rectangular wave 109 to the driving voltage 100, an electric charge stored in the storage capacitor 402 is reset (step 1). When the sampling switch 401 is turned on (connected to “1”) while the reset switch 404 is in an off state, an electric charge is supplied to the storage capacitor 402 at timing when the rectangular wave 109 has a “High” level (step 3). While (i) the sampling switch 404 is in an on state and the reset switch 404 is in the off state and (ii) the rectangular wave 109 has a “High” level again, an electric charge is stored again (step 6). After storage of electric charges is carried out more than once, measurement is carried out (step 7).
As has been described, when a fingertip etc. is placed between the driving electrode 100 and the sensing electrode 104, capacitance of the capacitor 105 changes (when the fingertip is placed, the capacitance of the capacitor 105 decreases). This causes a change in output voltage 402. The change is detected, so that whether or not a touch of the fingertip is present is detected.
Patent Literature 2 discloses an electrostatic capacitive touch panel (in-cell touch panel) integrated with a color filter on which substrate electrodes for detecting a touched position are provided. FIG. 16 is a diagram schematically illustrating a color filter integrated touch panel disclosed in Patent Literature 2.
In FIG. 16, the reference numeral “50” represents a touch panel integrated color filter which is integrated with electrode sections 60 and 70 for detecting a touched position. The touch panel integrated color filter 50 includes (i) a base material 52, (ii) “a color filter layer 54 including a plurality of colored sections 56” provided above the base material 52, and (iii) the electrode section 60 provided between the color filter layer 54 and the base material 52. The electrode section 70 is provided via an electrically-insulating layer 67 above a first surface of the electrode section 60 which first surface is opposite to a second surface of the electrode section 60 which second surface faces the base material 52. The electrode sections 60 and 70 are electrically connected to a circuit for detecting a contact position at which a fingertip etc. comes into contact with a display surface on a viewer side.
According to a conventional example illustrated in FIG. 16, a touch panel for detecting a touched position is integrated with the color filter on the color filter substrate. It is possible to realize a liquid crystal display device provided with a compact touch panel, the liquid crystal display device eliminating the need for additionally using another touch panel.
Patent Literature 3 describes a sensor array which detects physical quantity of light etc. and carries out parallel driving. Patent Literature 3 describes that an optical sensor is employed as a sensor. The technique described in Patent Literature 3 is applicable to driving of an electrostatic capacitive touch panel.
FIG. 17 is a diagram illustrating a sensor array device described in Patent Literature 3. A two-dimensional sensor array 19 includes (i) a plurality of row electrodes, (ii) a plurality of column electrodes, (iii) pin diodes provided at respective intersections where the plurality of row electrodes intersect the plurality of column electrodes, the pin diodes converting light into electric current, (iv) a driving section including a first shift register 17, a first analog switch 18 and the like, and (v) a detection section including a second shift register 21, a second analog switch 22 and the like.
The two-dimensional sensor array 19 is driven by simultaneously (concurrently) applying an M-sequence signal via the first shift register 17 and the first analog switch 18 to the plurality of column electrodes of the two-dimensional sensor array 19, the M-sequence signal being generated by a first M-sequence signal generator 16. The two-dimensional sensor array 19 detects physical quantity (of light) by (i) sequentially selecting the plurality of row electrodes with the second analog switch 22 and (ii) detecting detection electric currents of optical sensors at intersections where a selected row electrode intersects the respective plurality of column electrodes. A detection output is written in a frame memory 26 via a first correlator 25. Data written in the frame memory 26 is (i) subjected to matrix conversion, (ii) read out, (iii) supplied to a second correlator 27, (iv) computed by the second correlator 27, and then (v) outputted as a restoration output.
Patent Literature 4 describes an electrostatic capacitive touch panel which carries out parallel driving. FIG. 18 is a diagram schematically illustrating the touch panel described in Patent Literature 4.
As illustrated in FIG. 18, a sensor section 100 that constitutes the touch panel includes (i) a plurality of transmission conductors 12 each extending in an X-axis direction and (ii) a plurality of reception conductors 14 each extending in a Y-axis direction. The plurality of transmission conductors 12 simultaneously (concurrently) receive diffusion signs from a diffusion sign supplying circuit 21. The diffusion signs are simultaneously detected by the plurality of reception conductors 14.
A detection output is supplied to a correlation value calculating circuit 34 via a reception conductor selecting circuit 31, an amplifying circuit 32, and an A/D converting circuit 33. A correlation value obtained from the correlation value calculating circuit 34 corresponds to a detection state of a touched position. From the detection state, a position detecting circuit 35 calculates the touched position. Patent Literature 4 describes that a specific example of the diffusion signs is Hadamard sign.
The parallel driving disclosed in Patent Literatures 3 and 4 makes it possible to remarkably shorten a sensing period of a touch panel. It is therefore possible to shorten time intervals for detection of a touched position. That is, it is possible to detect the touched position with a further excellent response. In a case where the sensing period is constant, the number of times of integral can be increased. This can improve an S/N ratio. For example, assume that the number of times of integral was multiplied by M. In this case, the S/N ratio can be multiplied by √M.
Non-Patent Literature 1 discloses a semi in-cell electrostatic capacitive touch panel that includes a common electrode (Vcom electrode) of a liquid crystal display device and a driving electrode of the touch panel. The touch panel and a driver for driving the Vcom electrode are provided on a glass substrate so that the driver extends along a side part of the touch panel.
FIG. 19 is a diagram illustrating the semi in-cell touch panel described in Non-Patent Literature 1. A “Vcom driver” is provided in a left side region of the touch panel, and a “Vdriver” is provided in a right side region of the touch panel (see FIG. 19).